1. Field of the Invention
The present invention relates to a surface shape sensor utilizing a change in electrical characteristics caused when touched by an object surface, an identification device using this sensor, and a protected system using this device.
2. Description of the Related Art
As the society is highly information-oriented, the volume of information dealt with is more and more increasing. Most of these pieces of information must be treated as confidential information.
This leads to a recent growing interest in identification devices aiming at management of visitors at significant facilities and the like. Of these identification devices, those that utilize fingerprint for identification are often used.
Various types of identification devices utilizing fingerprint have been proposed. Most common devices are those having a fingerprint input unit for optically detecting a fingerprint as two-dimensional image signals. Other than this type, several devices have been proposed that detect a pressure corresponding to the projection/recess of the skin surface of a finger as a two-dimensional image signal.
Meanwhile, a method is proposed wherein a one-dimensional projection signal (fingerprint data) in the longitudinal direction of a finger is constituted from image signals of the entire finger, and this one-dimensional projection signal is output as the feature amount of the finger and used as an identification signal ("Identification Scheme Using Features of Finger" by Takeda, Uchida, Hiramatsu, and Matsunami in Technical Research Report of the Institute of Electronic, Information, and Communication Engineers of Japan: PRU89-50).
According to this report, since the one-dimensional projection signal is used, the data volume can be decreased and the processing algorithm can be simplified as compared to a case wherein two-dimensional fingerprint image signals are used.
Hence, the signal processing speed is increased, and the time required for identification can be shortened. Also, according to this scheme, it is reported that an adverse effect of disconnection or the like of the projecting portion, e.g., the ridge, of the skin surface of a finger is small.
However, even with a fingerprint input unit using this scheme, when a fingerprint is input, two-dimensional image signals of the entire finger are first detected optically as described above or by a pressure array sensor, and a one-dimensional projection signal is obtained from the two-dimensional image signals.
In this case, a large volume of information is needed to generate the image signals of an entire finger, and a complicated algorithm is needed in signal processing for generating the projection signal, resulting in an increase in time spent for the whole signal processing.
Furthermore, when an optical image input unit is used, the entire finger is input by a single finger motion as an image signal, leading to a large, expensive image input unit.
As described above, with the fingerprint input unit of the scheme wherein the one-dimensional projection signal in the longitudinal direction of a finger is constituted from image signals of the entire finger and this one-dimensional projection signal is output as the feature amount of the finger and used as the identification signal, a large volume of information is required to obtain the fingerprint image signals of the entire finger, and the complicated algorithm is needed in signal processing for obtaining the projection signal from the fingerprint image signals, leading to an increase in time spent for the whole signal processing.